Resistance of Diamondback Moth (Lepidoptera: Plutellidae) to a Combination of Fenvalerate and Piperonyl Butoxide

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Abstract
Pyrethroid and carbamate resistance persisted longer than organophosphorus resistance when selection pressure on diamondback moth, Plutella xylostella (L.), larvae was relaxed. Selection with fenvalerate and a mixture of fenvalerate and piperonyl butoxide (PB) resulted in the development of high levels of resistance to selection agents within a few generations. Thus selected, the diamondback moth had strong cross-resistance to three other pyrethroids (i.e., permethrin, cypermethrin, and deltamethrin) while cross-resistance (if any) to several organophosphorus insecticides was slight. PB, a microsomal oxidase inhibitor, lost its synergistic action with fenvalerate and permethrin in diamondback moth resistant to the mixture of fenvalerate and PB. The synergist MGK 264, another microsomal oxidase inhibitor, still retained its synergistic action. Selection with fenvalerate plus PB apparently caused development of resistance to the synergistic as well as toxic action of PB. Possible causes of this resistance are described, and implications of these phenomena in the chemical control of the diamondback moth are discussed.